In the wake of an evolution of digital devices in recent years, a variety of signal processing circuits, which had been conventionally realized by analog circuits, have been realized by digital signal processing.
In digital signal processing, various processes are realized by using a digital signal sequence which is obtained by sampling upon discretization an input signal to be quantized by digital values. In a linear time invariant system which is commonly used in general, because a sampling time interval is assumed to be constant, digital signal sequences whose sampling time intervals vary cannot be equally processed.
The sampling rate conversion calculating apparatus (or resampling system) is an apparatus for converting a sampling time interval of a digital signal sequence. A conventional sampling rate conversion calculating apparatus comprises an interpolation processing section for narrowing a sampling interval (an inverse number is referred to as a “sampling frequency”) to one integer-th thereof and a decimation processing section for lengthening a sampling interval to an integral multiple thereof (for example, refer to patent document 1). FIG. 15 is a block diagram illustrating a configuration of the conventional sampling rate conversion calculating apparatus. In FIG. 15, the conventional sampling rate conversion calculating apparatus comprises an input terminal 301, an interpolation processing section 302, a signal line 303, a decimation processing section 304, and an output terminal 305.
A digital signal sequence inputted to the interpolation processing section 302 is outputted from the signal line 303 as a signal whose sampling interval is narrowed to one integer-th thereof through interpolation processing. In the digital signal sequence which has been interpolation-processed, a data amount of a sample point is increased by a multiple of the narrowed sampling interval. In order to decimate the increased data amount, the decimation processing section 304 adjusts the data amount by lengthening the sampling interval of the digital signal sequence to an integral multiple.
By performing a series of these processes, the conventional sampling rate conversion calculating apparatus converts a sampling interval with a rational number ratio for the digital signal sequence inputted from the input terminal 301 and outputs from the output terminal 305 the digital signal sequence obtained after the conversion.
Patent document 1: Japanese Laid-Open Patent Publication No. 8-46484